S. Simon

Babeş-Bolyai University, Klausenburg, Cluj, Romania

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Publications (180)217.15 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Well-defined calcium molybdate (CaMoO4) and hydroxyapatite (HAP) nanocrystals were developed by thermal treatment on the surface of a SiO2–CaO–P2O5–MoO3 amorphous precursor synthesised at room-temperature by sol–gel route. The structural and morphological characterisaions were performed by several techniques: energy dispersive X-ray spectroscopy, thermal analyses (DTA/TGA), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy, electron paramagnetic resonance. Complementary, Fourier transform infrared and Raman spectroscopies provided a clear picture regarding the short range order structure, emphasising beside the CaMoO4 phase development, the presence of HAP nanocrystals. The vibrational spectroscopic techniques proved to be valuable tools for evidencing very small HAP nanocrystallites that cannot be clearly observed by XRD and TEM analyses.
    Journal of Materials Science 01/2015; 50(2). · 2.31 Impact Factor
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    ABSTRACT: The synthesis procedure represents a key aspect in designing the physical and chemical prop-erties of gold nanoparticles. The current study pro-poses a simple approach for gold nanoparticles synthesis using non-thermal plasma. The novelty of the setup consists in producing an in-liquid plasma discharge in argon bubbles that are externally gener-ated in the solution exposed to treatment. Because plasma is the source of active species which are directly involved in gold reduction, no additional reducing agent was necessary. Collagen protein was used as capping agent. A plasma treatment of 10 min is sufficient for obtaining stable colloidal solutions with UV-Vis absorption maximum at 530 nm. Trans-mission electron microscopy images revealed prepon-derant spherical nanoparticles with dimensions in the range of 6–20 nm. The method of synthesis distin-guishes by its good reproducibility, facility, efficiency, and ability to generate stable colloidal nanoparticles after several minutes of plasma exposure.
    Journal of Nanoparticle Research 08/2014; · 2.18 Impact Factor
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    ABSTRACT: The formation of a calcium phosphate layer on the surface of the SiO2 -CaO-P2 O5 glasses after immersion in simulated body fluid (SBF) generally demonstrates the bioactivity of these materials. Grafting of the surface by chemical bonding can minimize the structural changes in protein adsorbed on the surface. Therefore, in this study our interest was to evaluate the bioactivity and blood biocompatibility of the SiO2 -CaO-P2 O5 glasses after their surface modification by functionalization with aminopropyl-triethoxysilane and/or by fibrinogen. It is shown that the fibrinogen adsorbed on the glass surfaces induces a growing of the apatite-like layer. It is also evidenced that the protein content from SBF influences the growth of the apatite-like layer. Furthermore, the good blood compatibility of the materials after fibrinogen and bovine serum albumin adsorption is proved from the assessment of the β-sheet-β-turn ratio. © 2014 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2014.
    Journal of Biomedical Materials Research Part B Applied Biomaterials 05/2014; · 2.31 Impact Factor
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    ABSTRACT: Protein adsorption onto solid surfaces is a common phenomenon in tissue engineering related applications and considerable progress was achieved in this field. However, there are still unanswered questions or contradictory opinions concerning details of the protein's structure, conformational changes or aggregation once adsorbed onto solid surfaces. Electron paramagnetic resonance (EPR) spectroscopy and site-directed spin labeling (SDSL) were employed in this work to investigate the conformational changes and dynamics of the tRNA-modifying dimeric protein MnmE from E. coli, an ortholog of the human GTPBP3, upon adsorption on bioactive glass mimicking the composition of the classical 45S5 Bioglass®. In addition, prior to protein attachment the bioactive glass surface was modified with the protein coupling agent glutaraldehyde. Continuous wave EPR spectra of different spin labeled MnmE mutants were recorded to assess the dynamics of the attached spin labels before and after protein adsorption. The area of the cw-EPR absorption spectrum was further used to determine the amount of the attached protein. Double electron electron resonance (DEER) experiments were conducted to measure distances between the spin labels before and after adsorption. The results revealed that the contact regions between MnmE and the bioactive glass surface are located at the G-domains and at the N-terminal domains. The low modulation depths of all DEER time traces recorded for the adsorbed single MnmE mutants, corroborated with the DEER measurements performed on MnmE double mutants, show that the adsorption process leads to dissociation of the dimer and alters the tertiary structure of MnmE, thereby abolishing its functionality. However, glutaraldehyde reduces the aggressiveness of the adsorption process and improves the stability of the protein attachment.
    ACS Applied Materials & Interfaces 05/2014; 7(10):7615-7625. · 5.90 Impact Factor
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    ABSTRACT: The “build-up” methodology of a composite photocatalyst is a critical issue regarding the showed photocatalytic performance, including the formation of intermediates. To investigate this issue TiO2/WO3/Au aerogel composites were obtained by sol–gel method and subsequent photoreduction (Au) with UV or visible light. The obtained composites’ photocatalytic activity and intermediate formation profiles were evaluated using phenol as a model pollutant. XPS/UPS, XAFS and DRS were used to uncover local coordination, surface chemistry (of the different types of atoms (Ti, W, O and Au) and the band-structure (band-gap, possible electron transitions) of the obtained nanomaterials. The intermediates’ evolution profile and structural peculiarities were successfully correlated and it was shown that each minor structural (bulk or surface) change has a significant impact on the photocatalytic activity and intermediate formation dynamics.
    Applied Catalysis B Environmental 04/2014; 148-149:589-600. · 5.83 Impact Factor
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    ABSTRACT: The “build-up” methodology of a composite photocatalyst is a critical issue regarding the showed photocatalytic performance, including the formation of intermediates. To investigate this issue P25/WO3/Au composites were obtained by impregnation (WO3) and subsequent photoreduction (Au) with UV or visible light. The obtained composites’ photocatalytic activity and intermediate formation profiles were evaluated using phenol as a model pollutant. XPS/UPS and DRS methods were used to uncover local coordination, surface chemistry (of the different types of atoms (Ti, W, O and Au) and the band-structure (band-gap, possible electron transitions) of the obtained nanomaterials. The intermediates’ evolution profile and structural peculiarities were successfully correlated and it was shown that each minor structural (bulk or surface) change has a significant impact on the photocatalytic activity and intermediate formation dynamics.
    Applied Catalysis B Environmental 04/2014; 147:508-517. · 5.83 Impact Factor
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    ABSTRACT: Nanostructured hydroxyapatite (HA)-iron oxide composites obtained by a wet-chemical method through co-precipitation were investigated with respect to the changes induced in the samples structure by progressive addition of iron, by thermal treatments carried out at 450 oC, 550 oC and 700oC, and by incubation in simulated body fluid. The structural changes were analysed by X-ray diffraction (XRD), electron paramagnetic resonance (EPR) and magic angle spinning nuclear magnetic resonance (MAS-NMR). After heat treatments, crystalline HA was developed in all samples, even in larger amount in those with iron, showing that iron acts as catalyser for HA development. The MAS-NMR results show as well that only a part of the iron atoms are uniformly incorporated in the HA structure by replacing of calcium. EPR results support that an important part of iron atoms are disposed in regions rich in iron that behave like superparamagnetic or magnetic particles distributed in HA matrix. The analyses carried out on 550 oC treated samples, after three days of immersion in SBF, point out a decrease of HA crystallites size and the appearance on particles surface of a new amorphous calcium phosphate layer.
    Ceramics International 03/2014; · 2.09 Impact Factor
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    ABSTRACT: In this Note, a novel sensitivity multiplication module was added to classical quartz crystal microbalance (QCM). The purpose is to increase QCM frequency shift without changing nominal frequency of the quartz crystal resonator or nominal frequency value delivered to the frequency counter. Allan deviance measurement confirms that the multiplication of the frequency shift is limited by the quartz crystal loads with direct effect in quartz crystal quality factor and oscillator stability. An experimental implementation of this new sensitivity multiplication module that can increase up to six times the frequency shift of the QCM was experimentally investigated using different load conditions.
    The Review of scientific instruments 02/2014; 85(2):026116. · 1.52 Impact Factor
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    ABSTRACT: Gossypol is a polyphenolic compound with a wide range of therapeutic properties. The incorporation of gossypol in a porous gadolinium-silica matrix was considered for both therapeutic effect and contrast in magnetic resonance imaging. The purpose of the study was to evaluate gossypol loading in silica-gadolinium particles prepared at different pH values, as a first step in designing new theranostic (therapeutic and diagnostic) compounds. Silicagadolinium particles of 98SiO2�2Gd2O3 (mol%) composition were prepared following the sol–gel route. The structure of the particles and their loading with gossypol were investigated by X-ray diffraction, dynamic light scattering, Brunauer–Emmett–Teller analysis, differential thermal analysis, Fourier transform infrared spectroscopy, electron paramagnetic resonance and X-ray photoelectron spectroscopy. All results confirmed the highest loading of gossypol on the surface of the particles synthesised at lower pH. The potential application in magnetic resonance imaging (MRI) of silica-gadolinium particles loaded with gossypol was tested through MRI measurements that showed improved contrast properties compared with the pristine silica-gadolinium particles.
    Journal of Sol-Gel Science and Technology 01/2014; · 1.66 Impact Factor
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    ABSTRACT: The development of novel biomaterials able to control cell activities and direct their fate is warranted for engineering functional bone tissues. Adding bioactive materials can improve new bone formation and better osseointegration. Three types of titanium (Ti) implants were tested for in vitro biocompatibility in this comparative study: Ti6Al7Nb implants with 25% total porosity used as controls, implants infiltrated using a sol-gel method with hydroxyapatite (Ti HA) and silicatitanate (Ti SiO2). The behavior of human osteoblasts was observed in terms of adhesion, cell growth and differentiation.
    Journal of Biological Engineering 01/2014; 8:14.
  • Journal of Composite Materials 01/2014; 48. · 0.94 Impact Factor
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    ABSTRACT: Bioactive glasses belonging to the 56SiO2:(40�x)CaO:4P2O5:xAg2O system, with x = 0, 2 and 8 mol% were surface functionalized with the protein coupling agent glutaraldehyde (GA) and further evaluated in terms of hemoglobin affinity. The bare and GA functionalized samples were investigated before and after protein attachment, by electron paramagnetic resonance (EPR) spectroscopy combined with spin labeling procedure. Methanethiosulfonate spin label was used to explore the local environment of β�93 cysteine in horse hemoglobin, in terms of spin label side chain mobility. EPR simulation methods were employed to quantify the rotational correlational times and fraction of the immobilized spin labels. The EPR absorption spectrum was further exploited to estimate the amount of hemoglobin loaded on the substrates. The surface elemental composition obtained by X�ray Photoelectron Spectroscopy revealed similar tendency in terms of surface coverage. Changes in surface architecture, i.e. changes in surface morphology after protein coverage, were observed by Scanning Electron Microscopy. It was concluded that GA improves the stability of protein attachment and induces polymerization of hemoglobin molecules.
    The Journal of Physical Chemistry B 12/2013; 117(51):16558. · 3.61 Impact Factor
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    ABSTRACT: Melt derived glasses of (1-x)B2O3∙xBi2O3 system with 0.1 ≤ × ≤ 0.875 were investigated by X-ray photoelectron spectroscopy (XPS) in order to evidence the structural changes that occur at the surface of bismuth borate glasses as Bi/B ratio increases from 1:9 to 7:1. The high resolution XPS spectra of O 1s, Bi 4f and B 1s photoelectrons emphasizes consistent changes in the vicinity of oxygen, and small changes around bismuth and boron atoms by increasing of Bi2O3 content. The deconvolution of O 1s spectra was used to investigate the Bi/B ratio effect on the number of bridging and non-bridging oxygens and the results obtained were discussed considering four components occurring from oxygen atoms implied in BOB, BOBi, BiOBi and BO/BiO bonds. From the deconvolution of Bi 4f high resolution spectra, four components related to Bi0 and bismuth atoms connected in bonds of BiOBi, BOBi and BiO types were identified. It was concluded that boron and bismuth play a network former role in the entire compositional range.
    Journal of Non-Crystalline Solids 11/2013; 379:35-39. · 1.72 Impact Factor
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    ABSTRACT: The study is focused on synthesis, investigation of the structural and morphological changes induced by MoO3 addition, and thermal treatment, as well as in vitro characterization of a new sol-gel derived SiO2 -CaO-P2 O5 bioactive materials. The obtained systems are composite materials consisting of nanocrystalline apatite, bioactive glass and CaMoO4 nanoparticles, which are of interest for both regenerative medicine and specific medical applications of the releasable molybdenum ions. The changes induced by the thermal treatments and MoO3 addition with respect to the structure and morphology were completed using differential thermal analysis\thermogravimetric analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, electron paramagnetic resonance, and Brunauer-Emmett-Teller. The biological performance of these materials was evaluated in vitro by performing bioactivity and biocompatibility tests. The bioactive properties in terms of hydroxyapatite layer formation on the biomaterial surface after simulated body fluid immersion were studied by XRD and SEM. To establish their biocompatibility, the biomaterials surface was functionalized with protein and the resulted sample was investigated using SEM, FTIR, and XPS. The obtained results suggest that the addition of molybdenum oxide in proper concentration improves the biocompatibility in terms of enhancement of protein adherence on Si-Ca-P surface due to CaMoO4 crystalline phase development and does not inhibit bioactivity. © 2013 Wiley Periodicals, 2013.
    Journal of Biomedical Materials Research Part A 10/2013; · 2.83 Impact Factor
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    ABSTRACT: The study is focused on synthesis, investigation of the structural and morphological changes induced by MoO3 addition and thermal treatment, as well as in vitro characterization of a new sol-gel derived SiO2 -CaO-P2 O5 bioactive materials. The obtained systems are composite materials consisting of nanocrystalline apatite, bioactive glass and CaMoO4 nanoparticles, which are of interest for both regenerative medicine and specific medical applications of the releasable molybdenum ions. The changes induced by the thermal treatments and MoO3 addition with respect to the structure and morphology were completed using DTA\TGA, XRD, SEM, EDX, XPS, FTIR, EPR and BET. The biological performance of these materials was evaluated in vitro by performing bioactivity and biocompatibility tests. The bioactive properties in terms of HAp layer formation on the biomaterial surface after SBF immersion were studied by XRD and SEM. In order to establish their biocompatibility, the biomaterials surface was functionalized with protein and the resulted sample was investigated using SEM, FTIR and XPS. The obtained results suggest that the addition of molybdenum oxide in proper concentration improves the biocompatibility in terms of enhancement of protein adherence on Si-Ca-P surface due to CaMoO4 crystalline phase development and does not inhibit bioactivity.
    Journal of Biomedical Materials Research Part A 10/2013; · 2.83 Impact Factor
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    ABSTRACT: The biocompatibility of nanostructured titanosilicate microspheres with different Ti/Si ratios was evaluated by probing the affinity of horse haemoglobin (Hgb) towards the samples surface, in terms of quantitative and conformational changes analysis. The samples morphology before and after protein adsorption was evaluated by Scanning Electron Microscopy (SEM). X-ray Photoelectron Spectroscopy (XPS), Electron Paramagnetic Resonance (EPR) on spin labeled protein and Fourier Transform Infrared (FTIR) spectroscopies were further used to achieve information concerning both the amount of attached haemoglobin and its secondary structure modifications upon adsorption. The obtained results suggest that nanostructured titanosilicate microspheres present a friendly surface for protein adsorption and an enhanced protein adherence with increase of silica content.
    Journal of Molecular Structure 07/2013; 1044. · 1.40 Impact Factor
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    ABSTRACT: The dissolution and surface layer changes of new xTiO2(100 − x)[4SiO2·CaO·0.3P2O5] sol–gel derived xerogels (0 ⩽ x ⩽ 20 mol%) have been investigated in Kokubo’s simulated body fluid (SBF). The ionic leaching rate was analysed by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). ICP-AES results showed a relatively fast dissolution of titanium free sample, with a high release of phosphorous and calcium ions in the first hour of incubation while the release of silicon ions continuously increased up to 6 h of immersion. The titanium dioxide addition up to 20 mol% differently influences the release of phosphorus, calcium and silicon ions, i.e. TiO2 strongly stabilises the phosphorus ions, to a lesser extent the calcium ions, and has almost no effect on the silicon ions release. The structural changes were evaluated using X-ray powder diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). The XRD results show that all samples remain mainly amorphous after immersion in SBF. The changes occurred in the surrounding of phosphorous and silicon ions are well reflected in FTIR spectra and they were correlated with the samples stability in SBF.
    Corrosion Science 07/2013; 72:41–46. · 3.62 Impact Factor
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    ABSTRACT: The effects of gamma radiation on the local structure of PVA membranes containing TiO2 were investigated by ESR and XRD methods. An intense ESR signal is observed after irradiation at 16 KGy dose. This signal appears only for irradiated samples and it is associated with the breaking of the polymeric chain, followed by local reorganization of the polymeric segments and the apparition of the unpaired electrons and free radicals. The intensity of the signal decreases with the concentration of TiO2, indicating a shielding effect of the dopand. That the modification of local order of the polymeric chains has been modified after irradiation is confirmed by XRD method.
    Central European Journal of Physics 06/2013; · 0.91 Impact Factor
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    ABSTRACT: Titania/tungsten (VI) oxide/noble metal (gold and platinum) composites were obtained by the means of selective noble metal photodeposition on the desired oxide’s surface (either on TiO2 or on WO3). The noble metal particles’ localization was proved by SEM-EDX, while their size with DRS and TEM. The influence of the noble metal nanoparticles’ position was investigated successfully on the light absorption properties, photocatalytic activity toward oxalic acid and photocatalytic hydrogen production. Major differences were observed in the photocatalytic performance of the catalysts in which only the position of the noble metal was changed. Consequently, highly active composites were obtained, that surpassed the reference catalysts’ (TiO2(Au), TiO2(Pt), WO3(Au), WO3(Pt)) oxalic acid degradation yield and were also quite active for photocatalytic hydrogen production
    Catalysis Today 06/2013; 208:19-27. · 3.31 Impact Factor
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    ABSTRACT: Aluminosilicate microspheres obtained by spray drying were investigated in prospect of their potential biomedical applications. The as-prepared microspheres are amorphous. TEM and AFM were used to examine the morphology of the samples before and after immersion in simulated body fluid (SBF). The local structure changes as a function of microspheres composition and due to their immersion in SBF were investigated by 29Si and 27Al MAS–NMR. After SBF immersion, the silica network partially depolymerised by hydration/hydroxylation and the completely changed aluminium environment suggest a phylosilicate-like structure. 31P MAS–NMR analysis evidenced phosphorus ions incorporated in a new crystalline phase developed during SBF immersion.Highlights► Aluminosilicate microspheres less than 20 μm were prepared by spray drying. ► Microspheres structure is modified after immersion in simulated body fluid (SBF). ► Silica network is partially depolymerized by hydration/hydroxylation in SBF. ► After SBF immersion the aluminum environment is completely changed. ► Apatite type nanocrystals grown on microspheres in SBF mark their bioactivity.
    Corrosion Science 04/2013; Corrosion Science, 54:299-306. · 3.62 Impact Factor

Publication Stats

337 Citations
217.15 Total Impact Points

Institutions

  • 1993–2014
    • Babeş-Bolyai University
      • Faculty of Physics
      Klausenburg, Cluj, Romania
  • 1991–2006
    • Universitatea Tehnica Cluj-Napoca
      • Department of Physics
      Klausenburg, Cluj, Romania
  • 2001–2002
    • University of Wuerzburg
      • Institute of Physical and Theoretical Chemistry
      Würzburg, Bavaria, Germany